SimonH

Is it wise/safe to put a catless downpipe on an otherwise standard (well, an ITG too) P1?
Are there any dangers from it running too lean? I assume the P1 ECU is remapped for lower octane UK fuel anyway but would decatting increase the risks at all?

Fat Boy

I have a decatted P1(full scoobysport) with ITG. It is not wise to run it on ordinary unleaded anyway - you can but it's not great for it, after decatting definitely not ( OK if you run out and need to get home fine but don't thrash it, drive gently)as the P1 is mapped to run lean especially in a couple of areas.
Run it always with SUL + Octane Booster (NF in my case)and you should be fine.
Gurus like John Banks recommend installing a Knock link to detect if you are getting detonation - it basically lights up allowing you to stop doing whatever is causing it. Best of all get it remapped - Tek 3 from John Banks or Bob Rawle Developments. BRD are much closer to you and advertise on here.